Carbon nanotubes (hereinafter, referred as to ‘CNT’) are generally prepared by arc discharge, laser ablation, chemical vapor deposition or the like.
However, the arc discharge and laser ablation are disadvantageously difficult to mass-produce, and involve excessive preparation costs and purchase costs of a laser apparatus.
Furthermore, chemical vapor deposition has problems in that a synthesis rate is very slow and CNT particles that are synthesized are excessively small in the case of using a vapor dispersion catalyst and there is a limit to mass production of CNT because a space use efficiency in the reactor is significantly reduced in the case of using a substrate-supported catalyst.
Improved methods for mass-producing CNT have been disclosed and examples thereof include a rotary kiln method for producing CNT by incorporating a catalyst in a rotating drum reactor and then adding a reaction gas thereto, and a method for synthesizing CNT using a fluidized bed reactor including forming a fluidized bed, in which a fluid medium flows when heated, in a reactor, and synthesizing CNT in the fluidized bed.
However, in accordance with these CNT mass-production methods, a reactive gas containing hydrocarbon gas, inert dilute gas and reducing gas to control CNT production reactions at high temperatures is incorporated in a reactor and a carbon source is thus converted into CNT and consumed in the reactor to produce double reducing gas (specific example, hydrogen gas) as a by-product. Accordingly, there is a need for a technical method to control a mix ratio of these gases to a predetermined level.
However, conventional methods using rotary kiln reactors and fluidized bed reactors have problems in that a conversion ratio of carbon source is at most 80%, in particular, the mixed gas emitted from the reactor is inevitably directly incinerated and the cost of raw materials is thus increased due to absence of a method for selectively disposing of the reducing gas produced as a byproduct, unit productivity is limited due to excessive equipment scale, and a great amount of carbon dioxide is emitted during incineration of waste gas.